SIZE AND POWER OF GUNS. By PAO the in troduction of large-grain slow-burning powder and of heavier projectile, had much increased the power of guns in proportion to calibre. .\t that, time the English had guns weighing about No tons, of 17.72-inch bore. firing a 2000-ponn projectile. with 11140 feet. per second velocity. In the United State:, to keep pace with this movement, a 1(3-inch gun was designed, to weigh tons, and to fire a 2400-pound projectile, with a velocity of 230U feet per second. This gun, when finished, was the most powerful ever The time elapsed since its design has, however, seen a reaction of opinion ml verse to the con striwtion of guns abi?ve 12-inch calibre, and the experience of several recent wars, meagre as it has been. has led to a strong sentiment in favor of a limit even lower.
l'atxclm.Es of Drsit:N. A gun has to with stand three kinds of stress: (1) A pressure radially outward; (2) a force tending to stretch the gun longitudinally; (3) transverse stress due to the weight of the parts of the gun on opposite sides of the 'milli of support. The first, tending to enlarge the bore. stretches the metal circum ferentially, and on account of the resistance of the outer layers compresses the inner parts radi ally. The powder pressure is at a maximum be fore the projectile has moved more than a few inches—due to sudden evolution of gas, restricted space. and resistance of rilling—and quickly falls
as the projectile moves forward. When the size of the interior of the gun and the conditions of loading arc determined. the intensity of the pres sure to be expected at each point along the bore is calculated and a pressure curve plotted. The tray is clear for the design of the gun as an engineering structure to withstand these known forces at the various points. The tube of a built up gun is strengthened by potting over it hot which when cool are of less diameter than the tube's exterior by an amount called the 'shrinkage.' The shrinkages are so calculated that at no time shall any portion of the metal be strained beyond its elastic limit, and that in ease of accidental high pressures bringing the gun tip to its limiting strength all the com ponent eylinders would reach their elastic limits Thus it is necessary to ealenlate the shrinkage and strength under the assump tion that the maximum powder pressure is acting, and again that no interior pressure is acting; i.e. the 'system at rest.'